Pharmacokinetics of thiopental in hyperthermia patients was studied and compared with the data from normothermic volunteers. The terminal half-life of hyperthermia patients were approximately 2-fold longer than normal volunteers, and production of its major metabolite, thiopental carboxylic acid was markedly slowed down. The levels of thiopental in hyperthermic patients remained elevated for up to 24 hours. Decreased rate of metabolism, probably due to damage to liver cells and enzymes during hyperthermia, and increased shunting of the drugs to fatty tissues during hyperthermia followed by slow secondary release appeared to be the most likely explanations.